There are some late 1960's models that took a water pump housing that is slightly smaller in diameter. These are rare -- but there are still a few out there (e.g. 1969 120 HP). This housing measures 5 1/4" in diameter. If you have a late 1960's model, please check the diameter on your current water pump housing just in case! If you have a stringer drive in the 1970's or later, this is the kit.